1. Field of the Invention
The present invention relates to an apparatus for driving an inductive load according to an instruction from an external controller.
2. Description of the Related Art
As disclosed in Japanese Patent No. 3482948, it is known that, in an apparatus that drives an inductive load such as solenoid, a heat protection arrangement is provided to prevent its power supply circuit from being overheated when the operation of the load deviates from a normal condition. In the disclosed apparatus, the power supply circuit consists of a number of output stages that are thermally decoupled from each other and a heat protection circuit is provided for each output stage.
According to another technique as disclosed in Japanese Patent Publication 7-67389, an external controller is used to control the inductive load driving apparatus when the external controller is communicated from the apparatus that the power supply circuit of the apparatus is being overheated.
In the aforesaid Japanese Patent, heat protection circuits are provided one-to-one correspondence to each output stage. Therefore, if use is made of a pair of power supply circuits that operate complementarily to each other to drive an inductive load, it would be necessary to provide a heat protection circuit to each of the complementarily operating power supply circuits. This arrangement results in a complex configuration. Further, if thermal coupling should exist between these power supply circuits, their heat protection circuits are likely to operate differently from each other, causing an error signal to be transmitted to the external controller.